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SubjectRe: [PATCH v18 15/32] mm/lru: move lock into lru_note_cost
On Mon, 21 Sep 2020, Hugh Dickins wrote:
> On Mon, 24 Aug 2020, Alex Shi wrote:
>
> > We have to move lru_lock into lru_note_cost, since it cycle up on memcg
> > tree, for future per lruvec lru_lock replace. It's a bit ugly and may
> > cost a bit more locking, but benefit from multiple memcg locking could
> > cover the lost.
> >
> > Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
>
> Acked-by: Hugh Dickins <hughd@google.com>
>
> In your lruv19 github tree, you have merged 14/32 into this one: thanks.

Grr, I've only just started, and already missed some of my notes.

I wanted to point out that this patch does introduce an extra unlock+lock
in shrink_inactive_list(), even in a !CONFIG_MEMCG build. I think you've
done the right thing for now, keeping it simple, and maybe nobody will
notice the extra overhead; but I expect us to replace lru_note_cost()
by lru_note_cost_unlock_irq() later on, expecting the caller to do the
initial lock_irq().

lru_note_cost_page() looks redundant to me, but you're right not to
delete it here, unless Johannes asks you to add that in: that's his
business, and it may be dependent on the XXX at its callsite.

>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: linux-mm@kvack.org
> > Cc: linux-kernel@vger.kernel.org
> > ---
> > mm/swap.c | 5 +++--
> > mm/vmscan.c | 4 +---
> > 2 files changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/swap.c b/mm/swap.c
> > index 906255db6006..f80ccd6f3cb4 100644
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -269,7 +269,9 @@ void lru_note_cost(struct lruvec *lruvec, bool file, unsigned int nr_pages)
> > {
> > do {
> > unsigned long lrusize;
> > + struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> >
> > + spin_lock_irq(&pgdat->lru_lock);
> > /* Record cost event */
> > if (file)
> > lruvec->file_cost += nr_pages;
> > @@ -293,15 +295,14 @@ void lru_note_cost(struct lruvec *lruvec, bool file, unsigned int nr_pages)
> > lruvec->file_cost /= 2;
> > lruvec->anon_cost /= 2;
> > }
> > + spin_unlock_irq(&pgdat->lru_lock);
> > } while ((lruvec = parent_lruvec(lruvec)));
> > }
> >
> > void lru_note_cost_page(struct page *page)
> > {
> > - spin_lock_irq(&page_pgdat(page)->lru_lock);
> > lru_note_cost(mem_cgroup_page_lruvec(page, page_pgdat(page)),
> > page_is_file_lru(page), thp_nr_pages(page));
> > - spin_unlock_irq(&page_pgdat(page)->lru_lock);
> > }
> >
> > static void __activate_page(struct page *page, struct lruvec *lruvec)
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index ffccb94defaf..7b7b36bd1448 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1971,19 +1971,17 @@ static int current_may_throttle(void)
> > &stat, false);
> >
> > spin_lock_irq(&pgdat->lru_lock);
> > -
> > move_pages_to_lru(lruvec, &page_list);
> >
> > __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
> > - lru_note_cost(lruvec, file, stat.nr_pageout);
> > item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
> > if (!cgroup_reclaim(sc))
> > __count_vm_events(item, nr_reclaimed);
> > __count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
> > __count_vm_events(PGSTEAL_ANON + file, nr_reclaimed);
> > -
> > spin_unlock_irq(&pgdat->lru_lock);
> >
> > + lru_note_cost(lruvec, file, stat.nr_pageout);
> > mem_cgroup_uncharge_list(&page_list);
> > free_unref_page_list(&page_list);
> >
> > --
> > 1.8.3.1
> >
> >
>

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